1. Field of the Invention
The present invention relates to a luster resin molding, for example, a long resin molding having metallic luster or the like obtained by mixing metallic pigment, and a method of manufacturing such a molding. Particularly, such a molding can be used as an automobile side molding formed of luster resin and such a method can be used as a method of manufacturing such an automobile side molding.
The present application is based on Japanese Patent Application No. Hei. 10-128656, which is incorporated herein by reference.
2. Description of the Related Art
As for an automobile molding as such a conventional luster resin molding, a technique shown in FIG. 5 is known.
FIG. 5 is a sectional view of a conventional automobile molding taken perpendicularly to its longitudinal direction.
In the conventional automobile molding, a design surface 2 is provided on the front surface of a molding body 1 while a car-body attachment surface 3 is formed on the back surface. Two lines of double-side adhesive tapes 4a and 4b are pasted to the car-body attachment surface 3. A cross-shaped positioning boss 5 is provided between the double-side adhesive tapes 4a and 4b so as to project from the molding body 1. The positioning boss 5 is formed integrally with the back surface of the molding body 1.
The automobile molding is attached to a car body 7 in such a manner as follows. The positioning boss 5 is inserted into a positioning hole 8 of the car body 7. Pressure is applied to the molding body 1 in the state where the molding body 1 has been positioned onto the car body 7. The molding body 1 is fixed to the car body 7 by the adhesive force of the double-side adhesive tapes 4a and 4b. In the conventional automobile molding, therefore, since the positioning boss 5 is provided so as to project from the molding body 1, the molding body 1 can be attached to an accurate position of the car body 7 by the positioning boss 5.
Another technique disclosed in Japanese Utility Model Publication No. Sho. 62-95960 is also known as an automobile molding having such a positioning boss.
If the molding body 1 and the positioning boss 5 were formed integrally, however, the following problem was caused. The problem will be described about a case where the cross-shaped positioning boss 5 is formed integrally with the molding body 1 by way of example.
FIGS. 6A and 6B are explanatory views showing a relationship between the injection direction and distribution of metallic pigment when the positioning boss is formed integrally with the molding body 1. FIG. 6A is a front view in which the longitudinal direction extends right and left, and FIG. 6B is a top plan view in which the longitudinal direction extends right and left.
The flow of synthetic resin in the molding body 1 is affected by the flow of resin into the cross-shaped positioning boss 5A, so that the light distribution of metallic pigment near the cross-shaped positioning boss 5A to the molding body 1 is as follows.
As shown in FIG. 6A, the flow velocity of a boss supply flow n near the central line X--X before flowing into the cross-shaped positioning boss 5A does not change in comparison with that of a main flow m supplied by injection molding. However, the flow velocity of the boss supply flow n after flowing into the cross-shaped positioning boss 5A becomes slower than the main flow m supplied by injection molding because the flow in the longitudinal direction of the molding body 1 is affected by the volume of the positioning boss 5A. As a result, a flow-in phenomenon occurs in the downstream of the cross-shaped positioning boss 5A so as to compensate the main flow n supplied by injection molding. For example, in the downstream of the cross-shaped positioning boss 5A, the main flow n flows in the direction of the central line X--X of the cross-shaped positioning boss 5A. But, the flow velocity of the main flow n flowing in the direction of the central line X--X becomes slower than that on its opposite sides because of the volume supplied in the longitudinal direction of the cross-shaped positioning boss 5A, so that flow-in streams o and g is generated in the opposite sides. These flow-in streams o and g move round from the opposite sides of the positioning boss 5A, and then flow in the direction of the central line of the main flow n. The position where the flow-in streams o and g run against each other appears in the downstream of the cross-shaped positioning boss 5A.
Reduction of flow velocity caused by confluence of these flow-in streams o and g results in turbulence of distribution of synthetic resin blended with metallic pigment in the downstream of the cross-shaped positioning boss 5A. As a result, a black line p of a flow of synthetic resin appears in the downstream of the cross-shaped positioning boss 5A. Accordingly, the external appearance of the molding becomes bad.